Endoscopes are well-known optical imaging devices used for viewing objects within cavities or the internal surfaces of cavities, with additional capabilities of providing channels for insertion of devices to act upon or treat conditions of interest found. While the herein described invention has application in many fields, it has particular relevance to the medical field wherein flexible endoscopes are employed to view and treat deep and convoluted passages of the human body. In a typical endoscope designed for such purposes, the distal tip of the instrument is made maneuverable by employing four 90.degree. spaced quadrant cables which interact mechanically with a series of vertebrated or specifically profiled rings located adjacent to the distal end of the instrument. Bending and deflection of the rings is obtained by tensioning and relaxing the cables in accordance with controls located at the proximal end of the fiberscope on the control head. The means for applying tensioning and relaxing forces to these quadrant cables have been the subject of extensive technological effort resulting in controls such as joysticks or coaxial control wheels found on many well-known fiberscopes. The object of these efforts has been to provide on the control head of the endoscope cable tensioning and relaxing means accessible and comfortable to the hands and fingers, and, consistent with holding the scope, operating all other controls, and allowing such other manipulations of the endoscope (i.e., torque, pushing and pulling) as are deemed effective for the clinical procedure for which the endoscope was designed.
The prior art control mechanisms for the deflection of the distal end of endoscopes are designed for access partially by one hand or both hands of the operator manipulating the proximal head of the instrument. The method of control acts upon the four control cables in two pairs, treating as a pair two control cables which are spaced 180.degree. apart at a location of interaction with the aforementioned rings of the deflection system.
The prior art of more specific relevance to the invention herein discussed consists of designs embodying two coaxial control wheels mounted externally to the proximal control housing of the endoscope. The turning of one wheel at the head of the instrument acts to tension one cable of a pair of control cables while simultaneously releasing tension on the other cable in that pair of cables. The turning of the other control wheel acts similarly upon the other pair of control cables. The two wheels may be operated simultaneously.
As an aid in fixing the deflected distal endoscope section in a particular desired oposition, the deflection controls at the head of the instrument have included means to fix the control wheels in a particular position. One prior art means to accomplish this includes friction devices applied such as to place drag on the control wheels. For example, an operator wishing to place drag on the deflection control wheels actuates a lever or other device controlling the drag. Light drag or heavy drag results from the position selected for the drag control lever.
If some intermediate drag is desired, an intermediate position of the drag adjusting lever is selected. A specific desired or useful amount of drag can be determined only by trial and error involving setting of the drag control lever, turning the control wheels, resetting the lever closer to the optimum setting, again trying the wheels, etc. The same time-consuming exercise is required for the second wheel, and if the free running position is reestablished for any reason, the whole trial and error process must be repeated when next a drag mode is desired. In practice, this procedure results in acceptance of the initial setting of the drag control lever and attempting to work under less than optimum conditions.
Another prior art drag control applies a fixed amount of friction drag upon actuation of a control device. A disadvantage of prior art drag systems for endoscope deflection devices, which apply a friction effect either adjustably or fixedly, is an inability to achieve precise and predictable incremental movements of the deflection control. When pressure to turn a control wheel is applied, the drag is suddenly overcome, the wheel turns and, upon conscious release of turning pressure, the wheel stops turning and the instrument tip stops deflecting at a position sometimes not far enough, sometimes too far, sometimes just right, but generally at an imprecise and unpredictable position. This tendency to overshoot or undershoot a desired position calls for time-consuming maneuvers or alternatively calls for the use of both hands in attempting to minimize the over-undershoot effect.
Another disadvantage of prior art control wheel drag designs for deflection of control wheels is the negative effect on the degree to which the proximal deflection controls of the endoscope can be controlled with one hand. Ideally, the left hand holds and controls the proximal control head of the endoscope while the right hand is on the flexible insertion tube of the instrument controlling pushing and pulling and applying left or right torque to the shaft end of the endoscope.
The prior art drag designs require that the right hand be used far more often to achieve and hold the exact deflection position than is desirable. As a result, the right hand must move quickly to and from the shaft of the endoscope to again hold the desired next deflecting position and the next and the next in a series of repeated movements tending to interfere with the smooth progress of the insertion of the instrument into the body cavity. If the right hand is required to achieve each of these precise solutions, its function on the flexible shaft of the scope is continually interrupted. Removing the right hand from the flexible shaft often loses a desired tip position and time is lost in recovering that position.
In another prior art endoscope of substantially smaller size, specifically a bronchoscope having deflection in one plane only and incorporating only one pair of tensioning and relaxing cables, a toothed wheel inside the control housing interacts with a spring member to provide deflection increments. In attempting to adapt this construction to much larger endoscopes having more than one deflection wheel for polydirectional control, it was found that the space and strength requirements of the larger scope were such as to preclude adaptions of such control inside the control head of the endoscope. This is particularly so when each deflection control wheel is to be capable of providing either continuous mode deflection or incremental mode deflection and further when such selection is to be exercisable with a single hand. It became evident that a further disadvantage of an interior mounted incrementing and mode selection mechanism resides in the need to disassemble the endoscope whenever the mechanism needs adjustment.
In summary, the prior art approach to apply friction drag to the deflection control wheels of an endoscope deflection control generally encounters four main deficiencies:
(1) The setting of the desired amount of drag is imprecise and requires time with trial and error settings; PA1 (2) the drag system tends to be imprecise and unpredictable and positioning the endoscope distal tip because of the tendency to over or undershoot its next position; PA1 (3) the right hand is needed to minimize the foregoing negative effects and is, therefore, forced continually to be removed from its preferred flexibleshaft-holding location. As a result there is a general loss in hand-eye coordination in applying the endoscope instrument as it is employed through difficult intubation maneuvers; PA1 (4) the crowded interior and strength required of the control heads for large endoscopes inhibits the internal placement of devices for overcoming these deficiencies.